Congressional Democrats said yesterday that they will continue to demand the testimony of senior White House adviser Karl Rove about a range of sensitive policy matters even after he leaves the West Wing at the end of the month.

"Karl Rove's resignation will not stop our inquiry into the firings of the U.S. attorneys. He has every bit as much of a legal obligation to reveal the truth once he steps down as he does today," said Sen. Charles E. Schumer (D-N.Y.), who has helped lead the Senate Judiciary Committee's inquiry into the dismissals.

Rove's retirement announcement came 11 days after he refused to testify before the Judiciary Committee. While his actions figure in two other investigations on Capitol Hill, the Senate panel is the only committee that has subpoenaed Rove.

Aides to Judiciary Committee Chairman Patrick J. Leahy (D-Vt.) said he is considering whether to assert that a White House claim of immunity is not valid, which could lead to a committee vote next month holding Rove in contempt of Congress.

White House counsel Fred F. Fielding wrote in an Aug. 1 letter to Leahy that President Bush asserted that Rove, "as an immediate presidential adviser," was immune from testifying on any of his official activities. Fielding has offered to allow Rove and other current and former West Wing staff members to be interviewed behind closed doors, but not under oath.

Legal experts were divided on whether Rove's resignation heightens the likelihood of his testimony. Stanley Brand, former House general counsel, said the president's privilege claim will extend beyond Rove's days as a White House adviser. "He's too close to the king. This is the guy who's the king's alter ego," Brand said.

But Charles Tiefer, a constitutional scholar at the University of Baltimore, said some former White House staff members have testified in past confrontations, even though they claimed immunity while serving in the West Wing. Tiefer pointed to Oliver L. North, who refused to testify while still on President Reagan's National Security Council in 1986 but appeared in nationally televised hearings in 1987, after he had left the White House.

A rationale often used by White House staff members for refusing to testify is that it interferes with an official's ability to advise the president, Tiefer said. "He can no longer say that an appearance would compromise his ongoing White House duties. It becomes more and more untenable for him to refuse to show up."